This invention relates to an anti-blurring optical member to be used for window pane, reflecting mirror, etc. in automobiles and other vehicles, ships and boats, air-crafts, and buildings.
In the past, there has been a problem with water droplets adhering onto glass or the like which is used in the window panes and reflecting mirrors in the vehicles, ships and boats, air-crafts, and buildings and thereby deteriorating visibility through it.
In an attempt to eliminate the problem, the art has employed: (1) treatment of the glass surface to render it hydrophobic; and (2) treatment of the glass surface to render it hydrophilic, wherein each of the methods are designed to change the surface energy, in principle.
As to the method for rendering the glass surface hydrophobic, there is, on the one hand, a method, by which an organic silicone type or a fluorine type hydrophobicizing agent is coated on the surface of the optical member by application or spray; and, on the other hand, a method, by which a polymerized film of a fluorocarbon type or a fluorine type is coated on the surface of the optical member by the plasma-polymerization method (see Japanese Patent-Kokoku Publication No. 60-13065). Still further, a method, where the surface of the optical member is reformed by the ion-injection method, has been when the optical member is comprised of an inorganic glass.
There are various methods for treating the glass surface to render it hydrophilic, such as: (1) a method of coating the surface of the optical member with a hydrophilic surfactant, a polyhydric alcohol, or a hydrophilic polymer; (2) a method of coating the surface of the optical member with an inorganic compound such as MgF.sub.2, CaF.sub.2, SiO, and so forth; and (3) a method of subjecting the surface of the optical member to the ion-etching, in the case where the optical member is of inorganic glass; and others. Each of these methods seeks to secure the viewing field by the perfect wetting of the surface of the optical member.
However, the surface of the optical member which has been subjected to the hydrophobic treatment has a maximum contact angle of 110.degree., hence it does not always repel water drops perfectly therefrom. In the case where water drops are of a large size or they can be easily blown off by wind, the water on the glass surface readily flows, and a good viewing field can be secured. On the contrary, however, when very small drops of water adhere on the glass surface, they would inevitably remain on the glass surface to deteriorate the visibility.
On the other hand, while the surface of the optical member which has been subjected to the hydrophilic treatment has excellent light transmitting property in comparison with a non-treated surface, when water drops adhere on it, it permits a film of water to be formed over the entire surface thereof, and, depending on the kind of film, there may take place a phenomenon such that an image of an object viewed through the optical member is seen deformed. As such, it has occurred that the visibility of an object image through the optical member becomes poor, when very small drops of water covers the surface of the optical member, or when the film of water is formed on the surface of such member.